what engine are you running? Nitro's lose power around 30K don't they? Its been a few years since i ran nitro and i wasn't that big into it then. Lets just say that your motor hits peaks at 30K. Use a 3 cell at 3.7V each for 11.1 volts and then use 1515 1.5d motor (2700kv) to give you right around 30K rpm.